fix(cellNav): Don't setup when directive not there

The cellNav feature was attaching logic to render containers and grid
cells despite the uiGridCellnav directive not being on the parent grid
component. This was causing exception to be thrown during scroll events.

This change looks for the cellNav controller (which is simply
empty) and bails before attaching logic if the controller is not present.

Also added tests to cover the exceptions that were occuring.

Fixes angular-ui#2128

src/features/cellnav/js/cellnav.js

@@ -622,6 +622,7 @@
         priority: -150,
         require: '^uiGrid',
         scope: false,
+        controller: function () {},
         compile: function () {
           return {
             pre: function ($scope, $elm, $attrs, uiGridCtrl) {
@@ -696,15 +697,17 @@
       return {
         replace: true,
         priority: -99999, //this needs to run very last
-        require: ['^uiGrid', 'uiGridRenderContainer'],
+        require: ['^uiGrid', 'uiGridRenderContainer', '?^uiGridCellnav'],
         scope: false,
         compile: function () {
           return {
-            pre: function ($scope, $elm, $attrs, uiGridCtrl) {
-            },
             post: function ($scope, $elm, $attrs, controllers) {
               var uiGridCtrl = controllers[0],
-                  renderContainerCtrl = controllers[1];
+                  renderContainerCtrl = controllers[1],
+                  cellNavController = controllers[2];
+
+              // Skip attaching cell-nav specific logic if the directive is not attached above us
+              if (!cellNavController) { return; }
 
               var containerId = renderContainerCtrl.containerId;
 
@@ -765,9 +768,15 @@
       return {
         priority: -150, // run after default uiGridCell directive and ui.grid.edit uiGridCell
         restrict: 'A',
-        require: '^uiGrid',
+        require: ['^uiGrid', '?^uiGridCellnav'],
         scope: false,
-        link: function ($scope, $elm, $attrs, uiGridCtrl) {
+        link: function ($scope, $elm, $attrs, controllers) {
+          var uiGridCtrl = controllers[0],
+              cellNavController = controllers[1];
+
+          // Skip attaching cell-nav specific logic if the directive is not attached above us
+          if (!cellNavController) { return; }
+
           if (!$scope.col.colDef.allowCellFocus) {
             return;
           }

src/features/cellnav/test/uiGridCellNavDirective.spec.js

@@ -0,0 +1,26 @@
+describe('ui.grid.cellNav directive', function () {
+  var $scope, $compile, elm, uiGridConstants;
+
+  beforeEach(module('ui.grid.cellNav'));
+
+  beforeEach(inject(function (_$rootScope_, _$compile_, _uiGridConstants_) {
+    $scope = _$rootScope_;
+    $compile = _$compile_;
+    uiGridConstants = _uiGridConstants_;
+
+    $scope.gridOpts = {
+      data: [{ name: 'Bob' }]
+    };
+  }));
+
+  it('should not throw exceptions when scrolling when a grid does NOT have the ui-grid-cellNav directive', function () {
+    elm = angular.element('<div ui-grid="gridOpts"></div>');
+
+    $compile(elm)($scope);
+    $scope.$digest();
+
+    expect(function () {
+      $scope.$broadcast(uiGridConstants.events.GRID_SCROLL, {});
+    }).not.toThrow();
+  });
+});